Discolorations, or stains, of the dentition are traditionally classified into two main categories, extrinsic and intrinsic. Extrinsic discolorations are on the outer surface of the dentition and can be removed from the surface through the use of dental instruments or polishing abrasives. In contrast, intrinsic discolorations are located within the crystalline matrix of the enamel and dentin and are not removable through the use of conventional dental instruments or polishing abrasives.
Extrinsic discolorations or stains are usually superficial stains of the tooth surface resulting from the deposition of a film, pigments or calculus on the teeth. Many agents can cause such extrinsic discolorations including common substances such as coffee, tea, artificial food colorations, grapes, berries, smoking or chewing of tobacco, and the like. Stain intensity, and consequently ease of removal of the stains, are worsened by the penetration of the stain into tooth surface irregularities such as pits, cracks, grooves, exposed dentin, and bared root surfaces resulting from recession. The degree of difficulty of removal of the stain increases the deeper the penetration of the stain, with some stains penetrating to such a depth that the removal is extremely difficult or virtually impossible using current methods of stain removal.
Intrinsic discolorations can have many causes of either an endogenous or exogenous origin and may occur during or after odontogenesis. During the process of creation of the teeth, referred to as odontogenesis, the teeth may become discolored from changes in the quality or quantity of enamel or dentin, or from incorporation of discoloring agents in the hard tissues, and may be caused by many diseases and medications, such as tetracycline. Post-eruption discolorations occur when discoloring agents enter the dental hard tissues from either the pulp cavity or tooth surface and can be caused by trauma, aging, metals, dental materials, and contact with or ingestion of certain foods and beverages.
A commonly practiced technique for removing discoloration is the practice of external bleaching, often with hydrogen peroxide. However, known bleaching agents are able only to remove discoloring agents located within five to seven microns from the enamel surface due to the high inorganic content and limited permeability of the enamel. Thus intrinsic discolorations and deeply penetrating extrinsic discolorations are left untouched.
Many attempts have been made over the years to find a bleaching system capable of removing intrinsic and deeply penetrating extrinsic stains. Chemical reagents that have been tried include hydrogen peroxide, oxalic acid, pyrozone (hydrogen peroxide and ethyl ether), muriatic acid, and chlorine compositions, as well as bleaching agents such as a 30% superoxol (30% hydrogen peroxide stabilized by reducing the pH to 4.0-5.0) or a pyrozone (30% hydrogen peroxide and ethyl ether) used in conjunction with heat from a light source, such as a tungsten lamp, or a heated instrument or bleaching paddle. The addition of heat to accelerate hydrogen peroxide's bleaching action has made such systems capable of reacting fast enough for in-office use. However, side effects due to the increased reactivity can be quite painful and include inflamed or burned gingiva and lips, as well as significant post-bleaching tooth sensitivity.
In an effort to overcome these side effects, “cold bleaching” systems were developed. These systems used longer room temperature reaction times instead of shorter heat activated reaction times. In these cold bleaching systems, the hydrogen peroxide is thickened or gelled to allow the hydrogen peroxide to form a coating capable of remaining in contact with the teeth for an extended period of time. Although the cold bleaching systems eliminated the side effects of the application of heat, a number of office visits were still required to achieve satisfactory results and post-bleaching sensitivity still occurred.
Recently, as disclosed in U.S. Pat. No. 5,645,428 to Yarborough, lasers have been used in a two-step dental bleaching process in which first an admixture of a bleaching agent and a catalyst are applied to the teeth and then exposed to an argon laser light to activate the bleaching agent followed by a second application of an admixture of a bleaching agent and a catalyst followed by exposure to a CO2 laser. However, the use of the CO2 laser adds considerable cost to the process as well as greatly increasing the chances of incurring damage to the enamel surface of the teeth due to exposure to the CO2 laser.